Oceanologia (2018) 60, 378—389
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ORIGINAL RESEARCH ARTICLE
Impact of climate change on the Curonian Lagoon
water balance components, salinity and water
temperature in the 21st century
Darius Jakimavičius *, Jūratė Kriaučiūnienė, Diana Šarauskienė
Laboratory of Hydrology, Lithuanian Energy Institute, Kaunas, Lithuania
Received 6 July 2017; accepted 14 February 2018
Available online 1 March 2018
KEYWORDS Summary The Curonian Lagoon is a shallow water body connected to the Baltic Sea by a narrow
navigable strait, which enables an exchange of water of different salinity. The projected climate
Curonian Lagoon;
change together with the peculiarities of mixing water will undoubtedly alter hydrological regime
RCP scenarios;
of this lagoon. The study uses three climate model outputs under four RCP scenarios, four sea
HBV modelling
software; level rise scenarios and hydrological modelling in order to project the extent to which water
balance components, salinity and temperature may change in the future. In order to simulate
Water salinity;
river inflow, the Nemunas River hydrological model was created using HBV software. In general,
Water temperature
the changes of the lagoon water balance components, salinity and temperature are expected to
be more significant in 2081—2100 than in 2016—2035. It was estimated that in the reference
3 3
period (1986—2005) the river inflow was 22.1 km , inflow from the sea was 6.8 km , salinity (at
Juodkrantė) was 1.2 ppt and average water temperature of the lagoon was 9.28C. It was
3 3
projected that in 2081—2100 the river inflow may change from 22.1 km (RCP2.6) to 15.9 km
3 3
(RCP8.5), whereas inflow from the sea is expected to vary from 8.5 km (RCP2.6) to 11.0 km
(RCP8.5). The lagoon salinity at Juodkrantė is likely to grow from 1.4 ppt (RCP2.6) to 2.6 ppt
(RCP8.5) by the end of the century due to global sea level rise and river inflow decrease. The
lagoon water temperature is projected to increase by 2—68C by the year 2100.
© 2018 Institute of Oceanology of the Polish Academy of Sciences. Production and hosting by
Elsevier Sp. z o.o. This is an open access article under the CC BY-NC-ND license (http://
creativecommons.org/licenses/by-nc-nd/4.0/).
* Corresponding author at: Laboratory of Hydrology, Lithuanian Energy Institute, Breslaujos st. 3, LT444003 Kaunas, Lithuania.
Tel.: +370 8 37 401801; fax: +370 37 351271.
E-mail address: [email protected] (D. Jakimavičius).
Peer review under the responsibility of Institute of Oceanology of the Polish Academy of Sciences.
https://doi.org/10.1016/j.oceano.2018.02.003
0078-3234/© 2018 Institute of Oceanology of the Polish Academy of Sciences. Production and hosting by Elsevier Sp. z o.o. This is an open
access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
D. Jakimavičius et al./Oceanologia 60 (2018) 378—389 379
estuaries) is supposed to occur (Chen et al., 2016; Liu and
1. Introduction
Liu, 2014; Vargas et al., 2017). Less fresh water might
also reach such water bodies due to reduced river inflow
Lagoons represent a complex and unique coastal environ-
(Dailidienė and Davulienė, 2008; Jakimavičius and Kovalen-
ment which requires special attention in the context of
kovienė, 2010; Vargas et al., 2017). Water salinity of the
climate change (Lillebo et al., 2015). These water bodies
Curonian Lagoon also mainly depends on fresh (inflowing
are especially sensitive to any environmental changes. Water
from rivers) and brackish (entering from the Baltic Sea)
temperature and sea level rise that in turn leads to an
water exchange, which is a complex process with many
increase in water salinity are fundamental environmental
driving factors. Zemlys et al. (2013) developed a 3D model
descriptors that play a vital role in sustainability of lagoon
to reveal characteristic features of water exchange
ecosystems. Both of them are projected to change in the
between these two water bodies and related vertical and
future (Anthony et al., 2009).
horizontal salinity distributions. The later study (Umgiesser
The rise of sea surface temperature (SST) is tightly con-
et al., 2016) showed that the most important physical force
nected with the effects of climate change. According to
that influences the water renewal time in the Curonian
observation data beginning in 1880, the global ocean warms
1 Lagoon is the Nemunas River discharge. The investigation
by 0.0058C year (Huang et al., 2014; Liu et al., 2014).
by Dailidienė and Davulienė (2008) proved that the mean
Considerably stronger growth tendencies of SST were esti-
1 water salinity in the Klaipėda Strait and in the northern part
mated in 1986—2005: 0.028C year (Huang et al., 2015a).
of the Curonian Lagoon in 1984—2005 was increasing, but
SST in European seas is increasing more rapidly than in the
whether it is going to increase in the future has not yet been
global oceans. The rate of increase is higher in the northern
assessed.
European seas and lower in the Mediterranean Sea (Coppini
Sea surface temperature, level rise and salinity are closely
et al., 2007). The results obtained by Stramska and Biało-
related with each other and with water balance elements. All
grodzka (2015) also revealed that this process takes place
of these variables are changing and are expected to change in
slightly faster in inner and relatively close seas, e.g. according
the future as direct or indirect consequences of global
to the data of 1982—2013, SST increased from 0.03 to
1 climate warming. SSTand salinity have a considerable impor-
0.068C year in the Baltic Sea (depending on location). In
tance for marine organisms, may directly affect the state of
the 21st century, the generally expected warming of the annual
ecosystem, limit the number of species, and are very impor-
Mediterranean SST ranges from 0.458C in the RCP2.6 scenario,
tant for juveniles' incubation period. Surveys, such as the
through 1.158C in the RCP4.5 scenario and 1.428C in the RCP6.0
ones conducted by Gasiūnaitė (2000), Gasiūnaitė and Razin-
scenario, to 2.568C in the RCP8.5 scenario (Shaltout and
kovas (2002), have shown that zooplankton in the northern
Omstedt, 2014). The rises of global surface temperature by
part of the Curonian Lagoon is very sensitive to salinity
the year 2100 projected by the IPCC should range from about
variation. Effects of different salinity conditions on the
1.38C for RCP 2.6 to 4.48C for RCP 8.5 (IPCC, 2013).
abundance and community composition of some aquatic
According to the data of 1880—2009, the global mean sea
1 macrophytes and microorganisms in the Curonian Lagoon
level rise (SLR) was 1.6 mm year (Church and White, 2011).
were assessed by Kataržytė et al. (2017). Increased summer
As reported by Navrotskaya and Chubarenko (2013), over the
water temperature causes ongoing eutrophication and algae
past 150 years, the rate of SLR in the lagoons and coastal
blooms in the Curonian Lagoon. Harmful algal blooms in July—
1
areas of the Southeast Baltic Sea (1.7—1.8 mm year ) is
October result in the deterioration of water chemical para-
close to the SLR rate in the World Ocean. In the second half
meters, death of fish in the coastal zone and pollution with
of the 20th century, the rate of SLR in the lagoons and marine
toxins (Aleksandrov et al., 2015).
1
areas became stronger: up to 3.6 mm year in the Vistula
The Curonian Lagoon is regarded as a water body abundant
Lagoon and in 1959—2006 in the Baltic Sea, exceeding the
with fish, temporarily or permanently inhabited by around
rate of the global ocean SLR. Similar tendencies of water
50 fish species. This unique and valuable lagoon ecosystem is
level changes are identified for the Curonian Lagoon, but
going to experience the impact of climate change due to
they depend on the length of available data series. For
increased water salinity and higher water temperature.
—
example, in the period of 1986 2005 (the reference period), There is an increasing concern that this ecosystem may be
1
the Curonian Lagoon water level grew 1.64 mm year . If strongly modified or destroyed in the future by the projected
other data series are used (e.g. 1961—1990), the rate of this changes.
1
ė
growth may reach 4 mm year (Dailidien et al., 2011; This study intends to use climate model outputs under RCP
č č ū ė
Jakimavi ius and Kriau i nien , 2013). Projections of rela- scenarios and hydrological modelling in order to project the
fi
tive SLR indicate a statistically signi cant increase in mean extent to which water balance components, salinity and
sea level along the entire European coastline: by around temperature of the Curonian Lagoon will change in two
21 and 24 cm by the 2050s under RCP4.5 and RCP8.5 respec- future periods: 2016—2035 and 2081—2100.
tively to reach 53 and 74 cm by the end of the century The expected future changes were projected according to
(Vousdoukas et al., 2017). However, according to Grinsted a new set of scenarios (called the Representative Concentra-
et al. (2015), SLR is not uniform globally but is affected by a tion Pathways (RCPs)) presented in the Intergovernmental
range of regional factors: the median 21st century relative Panel on Climate Change Fifth Assessment Report (IPCC,
SLR projection is 80 cm near London and Hamburg, with a 2013). When climate model outputs of the new generation
relative sea level drop of 0.1 m in the Bay of Bothnia (near (Representative Concentration Pathways — RCP) scenarios
Oulu, Finland). are used, hydrological modelling may be applied to assess the
As a consequence of sea level rise, the increase of sea- future environmental changes that are likely to happen in
water intrusion to transitional water bodies (lagoons and case any scenario occurs.
380 D. Jakimavičius et al./Oceanologia 60 (2018) 378—389
water coming from the Nemunas River, salinity of the entire
2. Material and methods
Curonian Lagoon changes. According to the data of 1986—
2005, salinity in the Curonian Lagoon is 2.5 ppt at Klaipėda,
2.1. Study area
1.2 ppt at Juodkrantė, and less than 0.1 ppt at Ventė and
Nida.
The Curonian Lagoon is a shallow water body that is sepa-
rated from the Baltic Sea by a narrow, dune-covered sand spit
(the Curonian Spit) (Fig. 1). At its north end, the lagoon is 2.2. Methodology and data
connected to the Baltic Sea by the navigable Klaipėda Strait.
The east coast of the lagoon is low, forested wetland, part of Water balance of the Curonian Lagoon consists of the follow-
which forms the Nemunas River delta. ing components: river inflow (QR), precipitation on the sur-
The Curonian Lagoon is a territory of high international face of the lagoon (P), evaporation from the lagoon (E),
environmental value. The Nemunas delta has a regional park inflow from the sea (QBS) and outflow from the lagoon
status and belongs to the Ramsar Convention sites. The (QCL). The main steps for evaluation of projections of water
lagoon meets the requirements of the Bonn Convention balance components, salinity and water temperature of the
and is one of the most valuable and important bird areas Curonian Lagoon in the 21st century were (Fig. 2): 1. Adapta-
—
in Lithuania. In 1929, in a headland of the Nemunas delta tion of climate scenarios for Lithuanian territory according to
ė
Vent Cape, a famous Lithuanian ornithologist professor T. three climate models and 4 scenarios; 2. Evaluation of
Ivanauskas opened an ornithology station, where each year projections of water balance components of the Curonian
—
about 60 80 thousand birds are ringed. The Curonian Lagoon Lagoon according to climate scenarios for near (2016—2035)
fi
is famous for its abundance of sh as well. The Curonian Spit and far (2081—2100) future periods; 3. Evaluation of projec-
is declared a national park and is included in the UNESCO tions of water temperature and salinity in the 21st century.
World Heritage List. The data outputs of projected precipitation and air tem-
2
Č
The whole surface area of the lagoon is 1584 km ( er- perature were acquired from global climate models pre-
2
vinskas, 1972). Lithuania owns only 381.6 km of its northern sented in the Intergovernmental Panel on Climate Change
Ž
part ( ilinskas and Petrokas, 1998). The average depth of this Fifth Assessment Report (IPCC, 2013) according to a new set
shallow lagoon is 3.8 m. The greatest depth is in the northern of RCP (Representative Concentration Pathways) scenarios
ė
part, where the Klaip da Seaport is located and the water (Moss et al., 2010; van Vuuren et al., 2011). Values of the
territory is dredged up to 16 m. The total volume of the daily mean air temperature T (8C) and daily amount of
3
š
lagoon is 6.2 km (Gailiu is et al., 2001). The residence time precipitation P (mm) in the near-future (2016—2035) and
of lagoon water in the northern basin is about 77 days, while far-future (2081—2100) periods were estimated according to
the average for the southern basin is nearly 200 days (Umgies- three climate models (GFDL-CM3, HadGEM2-ES, NorESM1-M)
ser et al., 2016). and four RCP scenarios (RCP2.6, RCP4.5, RCP6.0 and RCP8.5).
3 1
On average, the Nemunas discharged 22.1 km year of The climate model cells are large (up to 2.5 1.8958). Since
fresh water to the eastern part of the lagoon in the period of Lithuanian territory falls into 5 climate model cells, P and T
— fl
1986 2005. Depending on the ratio of brackish water in ow values derived from the climate models were recalculated
ė
from the Baltic Sea through the Klaip da Strait and fresh for 16 meteorological stations using the quantile mapping
Figure 1 Location of the Curonian Lagoon and measurement stations.
D. Jakimavičius et al./Oceanologia 60 (2018) 378—389 381
Figure 2 The principal scheme of the study.
statistical downscaling method (Teutschbein and Seibert, where P is the precipitation, E is an evaporation, Q is the
2013). runoff, SM is the soil moisture, SP is the snow pack, UZ is an
The nonparametric empirical quantile method is based on upper groundwater zone, LZ is the lower groundwater zone, V
the concept that there is a transformation h, which can be is the lake or dam volume.
described by the following equation (Gudmundsson et al., The daily values of river discharges (Q) in the Nemunas
2012; Sunyer et al., 2015): catchment from 10 water gauging stations (WGS) as well as T
and P from 14 meteorological stations (MS) (Fig. 3) were
Obs CM RP Obs 1 CM RP CM Fut
¼ ¼ ;
St h St ECDF ECDF St (1) necessary for model creation. Information about the mod-
elled catchment area, the presence of lakes and forests,
Obs CM RP
where St is an observed meteorological parameter, St
mean elevation (above sea level) of the area, WGS and MS
Obs
is the climate model output for the reference period, ECDF
was required as well. The created hydrological model was
is an empirical cumulative distribution function for the ob-
calibrated according to the data of 1986—1995 and validated
CM RP
served period, ECDF is an empirical cumulative distribu-
using the data of 1996—2005. The projection of the Nemunas
CM Fut
tion function for the climate model reference period, St
runoff at its mouth was estimated in daily steps for 2016—
is a meteorological parameter which is modelled by the
2035 and 2081—2100 using the calibrated model as well as the
climate model for the future period. All estimated results
output data from the selected climate models and RCP
— are compared with the values of the reference period (1986 scenarios.
2005).
The amount of evaporation and precipitation was calcu-
Estimation of the Curonian Lagoon's future water level was
lated using the data of Klaipėda, Nida and Šilutė MS. Input of
performed according to 4 sea water level rise scenarios which
each MS was evaluated according to the Thiessen polygon
project a water level rise of 0.44 m (RCP2.6), 0.53 m
method (Balany, 2011). The Thornthwaite equation was used
(RCP4.5), 0.55 m (RCP6.0) and 0.74 m (RCP8.5) from
to calculate the amount of evaporation (Thornthwaite,
2005 to 2100. Projections of the Curonian Lagoon's water 1948):
level for the periods of 2016—2035 and 2081—2100 were
a
accomplished using the lagoon level data (1986—2005) at 10 T m N
E ¼ 16 ; (3)
Juodkrantė and considering the water level rising tendencies I 360
described by the scenarios. 1
where E is the evaporation per month, (mm month ), T is
In order to simulate river inflow to the lagoon, the Nemu-
the mean monthly air temperature (8C), I is an empirical
nas River hydrological model was created using the HBV
annual heat index, a is an empirical I exponent, m is the
modelling software (Integrated . . ., 2005) based on the fol-
number of days in a particular month, N is the mean number
lowing water balance equation:
of sunny hours per month (depends on a latitude). This
d equation was introduced quite a long time ago, but recent
P E Q ¼ ½SP þ SM þ UZ þ LZ þ V ; (2)
dt comprehensive scientific studies (Jakimavičius et al., 2013;
382 D. Jakimavičius et al./Oceanologia 60 (2018) 378—389
Figure 3 Location of water gauging and meteorological stations in the investigated territory of the Nemunas River catchment.
the river inflow (QR). Monthly values of QBS and QR were
Lu et al., 2005) showed that it can still be successfully applied
estimated according to the multiannual water balance of the
to estimate the evaporation rate.
lagoon (1986—2005). Such structure of Eq. (7) was selected
Water exchange through the Klaipėda Strait was calcu-
deliberately. Large inflow from the Baltic Sea (QBS) increases
lated using a water balance method. A modified equation of
the salinity of the Curonian Lagoon, while significant inflow
water balance created by Gailiušis et al. (1992) was applied:
from the Nemunas River (QR) has an opposite effect. That is
ð þ Þ þ ¼ D ;
Q R P E Q exch V (4) why the ratio of these two variables was chosen. A constant
of 0.036 was selected in case if there is no inflow from the sea
in a particular (modelled) month, i.e. QBS = 0. Such cases may
occur in the presence of the significant discharge from the
> ; ¼ ;
if Q exch 0 Q exch Q BS (5)
Nemunas (e.g. during floods). These phenomena are very
rare: there were only 3 of them observed in 1986—2005. The
constant value of 0.036 is the least monthly salinity value
< ; ¼ ;
if Q exch 0 Q exch Q CL (6)
(ppt) in the lagoon at Juodkrantė in 1986—2005. The rest of
3
where QR is the river inflow, km , P is the precipitation on the constants (0.066, 0.635, 0.025 and 1.062) were generated
3
surface of the lagoon, km , E is an evaporation from the using the statistical software package Statistica 10.
3
lagoon, km , Qexch is the water exchange between the Cur- !
3 : 0:635
fl
onian Lagoon and the Baltic Sea, km , QBS is an in ow from 0 066 QBS
¼ : þ ;
3 3 SJ 0 036 1:062 (7)
fl D the sea, km , QCL is an out ow from the lagoon, km , V is the 0:025 Q
3 R
change in the volume of the lagoon, km .
Change of the Curonian Lagoon volume was estimated where SJ is the monthly water salinity at Juodkrantė, ppt; QBS
3
according to the water level projection. Daily volume is the monthly inflow from the sea, km ; QR is the monthly
3
changes and modelled river inflow were used to estimate river inflow, km .
flow discharges between the sea and the lagoon. Values of QBS The estimated correlation coefficient between the mea-
and QCL were assessed as a difference between the volume sured salinity values and the calculated ones according to
change in the Curonian Lagoon and the sum of river inflow. Eq. (7) was equal to 0.75. This coefficient is statistically
The negative discharge indicated a flow from the Curonian significant when p < 0.05.
Lagoon to the Baltic Sea, while the positive discharge showed To project the mean monthly water temperatures of the
a flow of the opposite direction. Curonian Lagoon, statistical relations between water and air
Projections of the Curonian Lagoon salinity were per- temperatures were created using the data of 1986—2005.
formed using statistical relations between water salinity at Water temperatures at Klaipėda, Juodkrantė, Nida and Ventė
Juodkrantė (SJ) and the ratio of inflow from the sea (QBS) and were calculated using the following equations:
D. Jakimavičius et al./Oceanologia 60 (2018) 378—389 383
ū Š š ė ū
TKW ¼ ð0:95 TKAÞ þ 1:02; (8) Nemaj nai to Smalininkai, e up , J ra, Minija and Nemu-
nas from Smalininkai to the Curonian Lagoon (Fig. 4).
The separate subbasins were merged together into a
TJW ¼ ð1:10 TNAÞ 0:31; (9) single Nemunas River runoff model. Each subbasin was cali-
brated separately, using the main sixteen calibration para-
meters which were adapted to each subbasin. The calibration
parameters were divided into four groups and calibration was
TNW ¼ ð1:13 TNAÞ 0:45; (10)
started from the first group parameters (volume changes).
The entire process of calibration is described in more detail in
(Integrated . . ., 2005; Kriaučiūnienė et al., 2013). The model
¼ : þ : ;
TVW 1 12 T Ï 0 29 (11) calibration was performed in the period of 1986—1995 (cor-
SA
relation coefficient (R) — 0.88, Nash—Sutcliffe efficiency
where TKW, TJW, TNW, TVW is the water temperature at (NSE) — 0.78, accumulated difference between the calcu-
ė ė ė 8
Klaip da, Juodkrant , Nida and Vent , C, TKA, TNA, TŠA is lated and the observed discharge (Accdiff) — 7.4%), while the
ė Š ė 8
an air temperature at Klaip da, Nida and ilut , C. model validation was carried out in the period of 1996—2005
—
Eqs. (8) (11) are valid only for the positive air tempera- (R — 0.75, NSE — 0.62, Accdiff — 5.7%) (Fig. 5). The created
8
ture. When air temperature reaches 0 C, it is assumed that in hydrological model was calibrated (1986—1995) and vali-
8
a given territory water temperature reaches 0.2 C and sta- dated (1996—2005) according to the observed hydrological
8
bilizes. This threshold water temperature (0.2 C) was esti- and meteorological data. Meteorological and water gauging
mated as an average of minimal monthly temperatures at station network, which data are used to develop the hydro-
ė ė ė —
Klaip da, Juodkrant , Vent and Nida in 1986 2005. logical model, are presented in Fig. 3.
Correlation between the values of air and water tempera- The calibrated model was then used to simulate the
tures was very high: from 0.98 (Eq. (8)) to 0.99 (Eq. (10)). Nemunas inflow to the Curonian Lagoon in a historical period.
fi fi <
These coef cients are statistically signi cant when p 0.05. In Fig. 6, the observed runoff values are compared to the
fi
Weighted coef cients for each WGS were estimated using simulated ones (the outputs of three climate models (average
the Thiessen polygon method. The mean water temperature of GFDL-CM3, HadGEM2-ES and NorESM1-M) for the period of
of the Curonian Lagoon was projected according to the 1986—2005). This modelling is necessary to perform in order
created statistical relations as well as air temperature pro- to find out how precisely the selected models reflect the
jections under three climate models and four RCP scenarios historical climate conditions. Since the hydrographs of the
— — for the periods of 2016 2035 and 2081 2100: observed and simulated historical runoff were very similar
3 1
(the mean annual discharges were 700 m s and
3 1
T ¼ ð0:006 T Þ þ ð0:066 T Þ þ ð0:160 T Þ
CLW KW JW VW 696 m s ), the selected climate models can be used for
future runoff simulation.
þ ð0:768 TNWÞ; (12)
where TCLW is the mean water temperature of the Curonian
3.2. Changes of water balance components of
Lagoon, 8C.
the Curonian Lagoon
3. Results
The water balance components of the reference period are
analyzed in Table 1. The water balance income consists of the
3 1
3.1. Calibration and validation of the Nemunas following components: river inflow (QR) — 22.1 km year
3 1
River runoff model (from 15.4 to 30.0 km year ), inflow from the sea (QBS) —
3 1 3 1
6.8 km year (from 5.4 to 9.0 km year ) and precipita-
3 1 3 1
When creating the Nemunas catchment hydrological model, tion (P) — 1.3 km year (from 0.9 to 1.7 km year ). The
the Nemunas River from the selected starting point (Druski- balance losses include outflow from the lagoon (QCL) —
3 1 3 1
ninkai) to the mouth (the Curonian Lagoon) was divided into 28.6 km year (from 20.9 to 36.8 km year ) and evapora-
3 1 3 1
separate parts sequentially attaching the catchments of: tion (E) — 1.0 km year (from 0.9 to 1.1 km year ). All of
Nemunas to Druskininkai, Merkys, Nemunas from Druskininkai these components have seasonal variation. The greatest
to Nemajūnai, Neris, Nevėžis, Dubysa, Nemunas from values of QR and QCL are characteristic for spring (April),
Figure 4 The scheme of the Nemunas River hydrological model.
384 D. Jakimavičius et al./Oceanologia 60 (2018) 378—389
Figure 5 Comparison of observed and simulated runoff of the Nemunas River in the periods of calibration (1986—1995) and validation
(1996—2005).
Figure 6 Comparison of observed average runoff at the mouth of the Nemunas River in historical period (1986—2005) with simulated
historical runoff according to average data of three climate models (GFDL—CM3, HadGEM2—ES and NorESM1—M).
while the smallest ones are observed in summer (July). On (RCP8.5), which, according to all four RCPs, constitutes an
the contrary, QBS is the smallest in spring (April) and the average decrease of only 0.7% if compared to the reference
largest at the end of autumn (November). E increases in value of 1986—2005. Inflow from the sea (QBS) is projected to
summer (July) and decreases in winter months, whereas P increase quite significantly (i.e. from 24.8% to 61.3%) due to
decreases in spring and is the most intensive in the autumn several reasons, including decreased river inflow (projected
season. to shrink from 0.1 to 28.2% according to different scenarios)
Fig. 7 outlines that under four RCP scenarios, the compo- and rising sea level (expected to grow by 0.44—0.74 m from
nents of the lagoon water balance are not expected to 2005). Inflow from the sea has seasonal patterns. The projec-
change significantly in the nearest future (2016—2035). tions indicate that it will get smaller by 3.4% in winter and
The analysis indicated that in this period, QR and QCL aver- greater by 4.5% in spring, on average, whereas in other
aged by all RCPs should decrease by 6.8% and 2.1% respec- seasons it will remain almost the same. Depending on the
tively, whereas QBS, E and P should increase by 13.9%, 10.8%, scenario, precipitation is expected to grow by 8.7—15.1%,
6.1% respectively in relation to the reference period (1986— while evaporation is expected to increase by 14.9—41.1% in
2005). comparison with the reference period amounts.
Considerably larger changes are projected in the far-
future period (2081—2100). QR is going to decrease from
0.1% (RCP2.6) to 28.2% (RCP8.5), and will on average be 3.3. Changes of the Curonian Lagoon salinity
13.4% smaller than in the reference period. QR values should
redistribute among the seasons. The greatest annual inflow
In the reference period, the average salinity of the Curonian
changes are projected in winter and spring. Q in winter is
R Lagoon at Juodkrantė (SJ) was 1.2 ppt. Its smallest values
expected to be greater from 1.9% (RCP2.6) to 10.3%
were observed in spring (0.5 ppt), while the largest ones
(RCP8.5), while Q in the spring season should get smaller
R were detected in autumn (1.9 ppt). The average annual
from 5.0% (RCP2.6) to 9.7% (RCP8.5) in comparison with the
salinity data at Juodkrantė demonstrates an upward trend
reference period. Because of rising global sea level and
equal to 0.08 ppt over a decade. The comparison of SJ values
decreasing river inflow, the water exchange through the
and both QR and QBS values presented in Table 1 indicated
Klaipėda Strait (Q and Q ) is expected to change. Q
CL BS CL that SJ at Juodkrantė is directly proportional to inflow from
3 3
should decline from 30.2 km (RCP2.6) to 26.5 km
the sea and inversely proportional to river inflow. Based on
D. Jakimavičius et al./Oceanologia 60 (2018) 378—389 385
Figure 7 Changes of the components of the Curonian Lagoon water balance (in % comparing projections of 2016—2035 and 2081—
2100 with average values of 1986—2005): (a) river inflow, (b) seasonal river runoff in 2081—2100, (c) inflow from the sea, (d) seasonal
inflow from the sea in 2081—2100, (e) precipitation on the surface of the lagoon, (f) evaporation from the lagoon.
3 1
Table 1 The water balance of the Curonian Lagoon in the reference period (1986—2005) (km year ).
Balance component Month Annual
I II III IV V VI VII VIII IX X XI XII
QR 2.4 2.2 3.0 3.2 1.8 1.2 1.1 1.1 1.1 1.4 1.7 1.9 22.1
QBS 0.6 0.4 0.4 0.2 0.4 0.6 0.5 0.6 0.6 0.8 0.9 0.9 6.8
P 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.1 1.3
Income 3.0 2.7 3.5 3.5 2.3 1.9 1.7 1.9 1.9 2.3 2.8 2.9 30.2
QCL 2.8 2.7 3.5 3.8 2.2 1.6 1.6 1.7 1.7 2.1 2.5 2.5 28.6
E 0.0 0.0 0.0 0.1 0.1 0.2 0.2 0.2 0.1 0.1 0.0 0.0 1.0
Losses 2.8 2.7 3.5 3.8 2.3 1.8 1.8 1.9 1.9 2.2 2.5 2.5 29.6
DV 0.0 0.0 0.0 0.0 0.1 0.0 0.0 0.0 0.0 0.0 0.0 0.1 0.1
Error 0.3 0.0 0.0 0.3 0.1 0.1 0.1 0.1 0.0 0.1 0.3 0.3 0.5
this dependence, Eq. (7) was created and used to estimate SJ (1.5 ppt), i.e. by 0.3 ppt larger than in 1986—2005. Fig. 8a
in the selected future twenty-year period (2016—2035 and presents that a greater variation is possible in summer and
2081—2100). autumn. During these seasons, salinity is projected to be
The projections revealed an increase of the lagoon water larger than in the reference period, while a smaller variation
salinity at Juodkrantė (Fig. 8) which can be attributed to is expected during the rest of the seasons. In winter and
changes of water exchange through the Klaipėda Strait and spring, salinity values will likely be similar to or somewhat
the Nemunas inflow. In the nearest future, the projected less than those in the past. At the end of the 21st century,
changes will probably be insignificant (up to 1.3 ppt, i.e. by salinity changes are projected to be more significant and
0.1 ppt larger than in the reference period) according to grow depending on scenario severity (they can reach as
RCP4.5 and RCP6.0 scenarios, whereas other scenarios indi- much as 2.6 ppt according to RCP8.5) (Fig. 8b). It is important
cate a slightly greater increase of the average salinity values to mention that these changes would occur in case of a
386 D. Jakimavičius et al./Oceanologia 60 (2018) 378—389
Figure 8 Projections of the Curonian Lagoon salinity (at Juodkrantė) in: (a) 2016—2035, (b) 2081—2100.
considerable decrease of the Nemunas inflow and rising sea temperature values according to the selected scenarios were
level. not identified; this variable is expected to grow by 1.78C on
average (Fig. 10a). As usual, in the far-future period, the
projected changes are going to be more significant: the mean
3.4. Changes of water temperature of the annual water temperature may grow by at least 2.38C
8
Curonian Lagoon (according to RCP2.6) or even by 6.3 C (according to the
most severe RCP8.5 scenario) compared to the reference
period values. On average, the annual water temperature is
Fig. 9 outlines the water temperature of the Curonian
8
Lagoon. Its annual variation at Klaipėda differs from the projected to be higher by 4.1 C than in the reference period:
8 8 8
one at Juodkrantė, Nida or Ventė. The reason for such it will rise by 2.3 C in winter, 4.2 C in spring, 5.0 C in summer
and 4.38C in autumn. The warmer lagoon water is likely to
phenomenon is the position of Klaipėda, i.e. it is located
at the junction of the sea and the lagoon. Since the volume of create unfavourable conditions for forming a permanent ice
the Baltic Sea is many times greater than the Curonian cover in winter.
Lagoon, its water warms up more gradually and cools down
slower. In the reference period, the average annual water
temperature was 8.88C at Klaipėda, 9.18C at Juodkrantė, 4. Discussion and conclusions
9.28C at Nida and 9.38C at Ventė. The average water tem-
perature of the entire Curonian Lagoon, calculated according The performed analysis presented in this paper attempted to
to Eq. (12) was 9.28C, which is very similar to the measured cover the full complexity of the potential impact of climate
one at Nida. This variable had an upward trend in the period change on the Curonian Lagoon water balance components,
of 1986—2005: it rose up by 0.78C at Klaipėda, by 0.88C at salinity and temperature. Projections were performed using
Nida, by 0.98C at Juodkrantė and by 1.08C at Ventė. It was three global climate models and four RCP scenarios. Values of
estimated that the average annual water temperature of the the projected variables were compared with the ones in the
Curonian Lagoon rose at an average rate of 0.04 degrees per reference period of 1986—2005. The estimated water bal-
year. ance of the Curonian Lagoon (in 1986—2005) and projections
Projections of water temperature of the Curonian Lagoon of the Nemunas inflow revealed that considerable variations
were performed using Eqs. (8)—(12) of four WGS and for two should be expected in the future. In all cases, the projected
selected future periods (Fig. 10). In the nearest future, changes are going to be much more significant in the second
considerable differences among the projected water period (2081—2100) than in the first one (2016—2035). In the
Figure 9 Water temperature of the Curonian Lagoon in the reference period (1986—2005).
D. Jakimavičius et al./Oceanologia 60 (2018) 378—389 387
Figure 10 Projections of water temperature of the Curonian Lagoon in: (a) 2016—2035, (b) 2081—2100.
nearest future, the Nemunas annual inflow may decline to than the rest of scenarios. These findings are in agreement
3
20.3 km (RCP2.6). In the far-future period, it is expected to with other results (Westervelt et al., 2015). The most likely
3
decrease to 15.9 km (RCP8.5), while in the reference period explanation of this is the increase of meteorological para-
3
it was 22.1 km . In the period of 2081—2100, considerable meters, such as air temperature and precipitation projected
seasonal redistribution of the Nemunas annual inflow is according to the RCP2.6 scenario until the middle of the 21st
expected. According to climate scenarios, the river inflow century, as well as the decrease of these variables that is
will increase by an average of 6.9% in winter and 0.8% in expected to occur in the second half of the century. In the
autumn, whereas it is expected to decrease by 7.1% in spring far-future period, the most significant changes of all inves-
and 0.5% in summer. Due to rising sea water level and smaller tigated variables are expected according to the RCP 8.5 sce-
amounts of river inflow, inflow from the sea annual input is nario.
3
expected to increase up to 8.0 km in the nearest future and This study does not rule out the presence of other factors
3
up to 11.0 km in the far future according to RCP8.5 (the that may have an influence on the state of the Curonian
scenario which projects the most drastic changes), while in Lagoon in the future. It is difficult to project anthropogenic
3
the past (1986—2005) it was 6.8 km . According to RCP8.5, activities, such as land use changes in river catchments,
the major changes of annual precipitation and evaporation Klaipeda Strait permeability changes, etc., that may alter
are likely to occur in the far-future period as well: evapora- the results of this study, creating a degree of additional
tion should intensify by 41.1%, while precipitation should uncertainty. However, there is a strong possibility that in
increase by 15.1%. the long term period (the end of 21st century), the projected
As inflow from the sea is expected to increase, the same changes will have the estimated tendencies.
will happen to salinity values. In the nearest future, salinity
at Juodkrantė is projected to reach 1.4 ppt on average (from Acknowledgments
1.3 ppt by RCP2.6 to 1.5 ppt by RCP8.5). At the end of the
century, salinity will gain significantly higher values: from
The authors are grateful to the Marine Research Department
1.4 ppt (RCP2.6) to 2.6 ppt (RCP8.5). On average, it is pro-
under the Environmental Protection Agency of Lithuania,
jected to reach 2.0 ppt, whereas the reference period value
which so kindly facilitated the salinity and water level
was 1.2 ppt. If future changes projected by RCP8.5 scenario
observation data necessary for this study.
come true, salinity would reach the reference values (2.6 ppt
This research is a part of a scientific study 'Impact Assess-
according to Dailidienė and Davulienė, 2008) of the Curonian
ment of Climate Change and Other Abiotic Environmental
Lagoon at Klaipėda (i.e. very close to the Baltic Sea). This
Factors on Aquatic Ecosystems' (project no. SIT-11/2015)
outcome is contrary to that of Vuorinen et al. (2015) who
funded under the National Research Programme 'Sustainabil-
found that unchanged salinity conditions at the end of the
ity of agro-, forest and water ecosystems (2015—2021)'.
21st century are possible as well.
In the reference period (1986—2005), water temperature
1
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